This invention relates to tail gas oxidizer units in a fuel cell system.
Fuel cells generate electrical power by reacting two fuel gas streams with each other. One of the gas streams is referred to as an anode gas while the other is referred as a cathode gas. Certain fuel cells use a stream of gas that is rich in hydrogen as the anode gas and an air stream as the cathode gas. When the fuel cell is in use, the hydrogen in the anode gas reacts with oxygen in the cathode gas to generate electrical power. Exhaust gases exiting the fuel cell may include un-reacted fuel gases, impurities contained within the fuel gas streams, and chemical products of the reactions in the fuel cell.
Multiple fuel cells are typically arranged in a stack. Fuel cell stacks are normally part of a system, known as a fuel cell system, that includes a fuel processor or reformer for generating one of the fuel gas streams. For example, the fuel cell system that includes the fuel cell of the example above may also include a reformer that reacts a hydrocarbon, such as methane, with water to produce the hydrogen rich stream. Certain fuel cell systems also include an anode tail gas oxidizer unit (ATO) where the exhaust gases from the fuel cell are, for example, reacted with oxygen to eliminate environmentally unfriendly chemicals from the exhaust.
In general one aspect of the invention relates to a fuel cell system that includes a fuel cell stack, which generates electrical energy during operation by reacting two reactant gases. The fuel cell stack also produces a fuel cell exhaust stream. An oxidizer unit is positioned to receive the fuel cell exhaust stream. The oxidizer unit oxidizes at least a part of the fuel cell exhaust stream in an oxidizing gas stream, such as air, during operation. A temperature sensor is positioned to sense a temperature of the oxidizer unit and an input system provides the oxidizer unit with at least the stoichiometric amount of the oxidizing gas stream during operation. The input system controls the amount of the oxidizing gas stream in excess of the stoichiometric amount provided to the oxidizer unit in response to the temperature of the oxidizer unit.
Embodiments of the invention may include one or more of the following features. The input system controls the amount of the oxidizing gas stream in response to the temperature of the oxidizer unit to maintain the temperature of the oxidizer unit at a target temperature. The input system includes a source, such as a blower, to provide the oxidizing gas stream, and a controller to control the amount of the oxidizing stream provided by the source in response to the temperature of the oxidizer unit. The temperature sensor generates a temperature signal corresponding to the temperature of the oxidizer unit and the controller includes a processor programmed to generate a control signal based on the temperature signal. The source provides the oxidizing gas stream in response to the control signal.
The controller stores a stoichiometric table for determining a stoichiometric amount of the oxidizing gas stream and uses the stoichiometric table when generating the control signal to direct the source to provide the oxidizer unit with at least the stoichiometric amount of the oxidizing gas stream. A meter measures an amount of electrical power generated by the system and generates a corresponding load signal. The stoichiometric table relates the load signal to a blower control signal that causes the blower to provide the oxidizer unit with the stoichiometric amount of the oxidizing gas stream. The controller uses the load signal and the stoichiometric table when generating the control signal to direct the source to provide the oxidizer unit with at least the stoichiometric amount of the oxidizing gas stream.
In general, another general aspect of the invention relates to a method that includes generating electrical energy in a fuel cell stack by reacting two reactant gas streams to produce a fuel cell exhaust stream, oxidizing at least a part of the fuel cell exhaust stream using an oxidizing gas stream in an oxidizer unit, sensing a temperature of the oxidizer unit, providing the oxidizer unit with at least the stoichiometric amount of the oxidizing gas stream, and controlling the amount of the oxidizing gas stream in excess of the stoichiometric amount provided to the oxidizer unit in response to the temperature of the oxidizer unit.
Embodiments of the aspect of the invention may include one or more of the following features. The amount of the oxidizing gas stream is controlled in response to the temperature of the oxidizer unit to maintain the temperature of the oxidizer unit at a target temperature. A temperature signal corresponding to the temperature of the oxidizer unit is generated and a control signal is generated based on the temperature signal. The oxidizing stream is provided in response to the control signal.
A stoichiometric table for determining a stoichiometric amount of the oxidizing gas stream is stored and used when generating the control signal to provide the oxidizer unit with at least the stoichiometric amount of the oxidizing gas stream. An amount of electrical power generated by the system is measured and a load signal corresponding to the amount of electrical power is generated. The stoichiometric table relates the load signal to the stoichiometric amount of the oxidizing gas stream and the control signal is generated based on the load signal and stoichiometric table to provide the oxidizer unit with at least the stoichiometric amount of the oxidizing gas stream.
Among other advantages, controlling the temperature of the anode tail gas oxidizer unit by, for example, maintaining the temperature at a target operating temperature controls the amounts of environmentally unfriendly chemicals in the oxidizer unit exhaust. Thus, the invention can be used to keep the amounts of environmentally unfriendly chemicals in the oxidizer exhaustbelow a threshold value.
The details of one or more embodiments of the invention are set forth in the accompanying drawing and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawing, and from the claims.